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Low Impact Development:

A Developer’s Guide to Innovative Stormwater

Management Techniques

CITY OF GREENFIELD

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Examples of LID Stormwater Management Techniques

VEGETATED SWALES AND FILTER STRIPS

Vegetated swales and filter strips work together to filter out pol-

lutants and treat and store runoff. Swales are vegetated open

channels that collect runoff from adjacent roadways or parking

lots and store and treat it. Swales can be used in subdivisions,

parking lots, and commercial and industrial development. Swales

work best when combined with a filter strip, which consists of

grass or close-growing vegetation that intercepts runoff from

surfaces, slowing it down and filtering out sediment and other

pollutants.

Greenfield’s Subdivision

Regulations encourage the use of

roadside swales and other LID

techniques.

Below graphic credit: MassDOT Separated

Bike Lane Planning and Design Guide

Developer’s Guide to Low Impact Development, City of Greenfield, MA

SITE PLANNING

Low Impact Development site planning seeks to minimize the

amount of stormwater runoff from the development in the first

place. Basic principles include building on previously disturbed

sites, reducing impervious surface area (design narrower,

shorter roads and driveways, avoid excessive parking, use per-

meable pavement/porous asphalt, etc.), minimizing tree clearing

and grading, and maintaining the natural topography of the site

by minimizing cut and fill. New subdivisions should site homes in

the least environmentally sensitive areas.

Greenfield’s Subdivision

Regulations call for

narrower roads that

conform to the existing

contours of the land.

Clustering homes in the

Rural Residential district

is encouraged, where

flexible lot sizes are

allowed in exchange for

protected open space.

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Examples of LID Stormwater Management Techniques

Developer’s Guide to Low Impact Development, City of Greenfield, MA

TREES

Trees in the built landscape offer many environmental and

quality of life benefits. Trees intercept rain on leaves and

branches, delaying and reducing peak flows. They absorb

groundwater through roots, increasing runoff storage capacity.

Trees shade pavement and buildings, reducing the urban heat

island effect and the costs and energy associated with cooling

buildings. Trees provide numerous other quality of life benefits,

including cleaner air, traffic calming, noise reduction, and in-

creased

Greenfield’s Subdivi-

sion Regulations, Zon-

ing Ordinance, and Tree

Ordinance seek to

minimize the removal

of mature trees during

development or

redevelopment

projects.

Graphic credit: Stormwa-

ter to Street Trees: Engi-

neering Urban Forests for

Stormwater Manage-

ment. U.S. EPA, 2013

Greenfield’s parking regula-

tions require a shade tree for

every ten (10) parking spaces,

to be distributed throughout

the parking lot for maximum

shading. The regulations also

require shade trees to be

planted within the perimeter

landscaped buffer between

the public right of way and the

parking area.

The value of street trees goes

beyond simple aesthetics. In

addition to benefits already

mentioned, neighborhoods

with mature street trees are

attractive places to walk, bike,

and be outside, improving pub-

lic health and helping to build a

sense of community.

Greenfield’s Subdivision Regu-

lations encourage street trees

to be planted in the tree belt.

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Examples of LID Stormwater Management Techniques

BIORETENTION / RAIN GARDENS

Bioretention / rain gardens are planted areas that collect, clean,

cool, and infiltrate stormwater and direct water to trees or other

desired plantings for birds and pollinators from roads, parking

lots, driveways, sidewalks, and roofs. Native plants and trees tol-

erant of drought and intermittent wet conditions, and occasional

salt from paved surfaces, should be used. In slowly permeable

soils a perforated underdrain may be installed at the bottom of

the excavation to prevent ponding. Routine maintenance can be

handled by homeowners or landscaping companies with proper

direction.

A bioretention area

located in the tree

belt can collect

stormwater runoff

from the sidewalk

and street.

Greenfield’s

Subdivision Regulations

encourage the use of

LID stormwater

features in new

Subdivisions.

Cul-de-sac islands

offer an opportunity

for collecting and

infiltrating stormwa-

ter. Greenfield’s Sub-

division Regulations

require a landscaped

island for all cul-de-

sacs.

Greenfield’s Zoning

Ordinance

encourages

bioretention for

parking lot medians

and islands.

Developer’s Guide to Low Impact Development, City of Greenfield, MA

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Examples of LID Stormwater Management Techniques

PERMEABLE PAVEMENT / POROUS ASPHALT / GRASS PAVERS

Permeable pavement / porous asphalt / grass pavers allow water

to filter through, recharging groundwater and reducing the

amount of runoff on a site. Permeable pavement or porous as-

phalt is appropriate for low traffic areas such as parking stalls,

overflow parking areas, sidewalks and walkways, and residential

driveways. Maintenance varies depending on the type of pave-

ment, and may include periodic vacuum sweeping, reseeding of

grass pavers, or refilling joint material.

Greenfield’s Zoning

Ordinance encourages

the use of porous

asphalt for parking stalls

and overflow parking

areas when feasible.

Developer’s Guide to Low Impact Development, City of Greenfield, MA

Paving stones, grass

pavers, and the use of a

“two-track” design are

allowed for residential

driveways.

STRUCTURAL SOILS

Structural soil is a mix of gravel and clay loam soil. The gravel

provides load bearing support for pavement while also providing

roughly 20% - 25% void space, which supports tree growth and

stormwater infiltration. Structural soils can work well in tree

belts and parking lot islands, extended out for 5-10 feet from

these points under impervious in parking lots, sidewalks, and pla-

zas, and are particularly effective when combined with perme-

able pavement or porous asphalt.

Greenfield’s parking

regulations encour-

age the use of struc-

tural soils in parking

lots.

Graphic credit:

Nina Bassuk, Urban

Horticulture Institute,

Cornell University.

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URBAN TREES AND THE USE OF STRUCTURAL SOIL

Urban trees experience a litany of environmental insults: soil

and air pollution, heat loads, deicing salts, and impacts from

utilities, vehicles, and buildings. The most significant problem

that urban trees face, however, is the lack of oxygen for their

roots, which is caused by a lack of tree root space, soil com-

paction, and poor drainage. Dense soil can also cause superfi-

cial rooting systems that cause pavement heaving and makes

the tree more vulnerable to drought.

Examples of LID Stormwater Management Techniques

ABOUT STRUCTURAL SOIL & HOW TO USE IT

Healthy trees need a large volume of non-compacted soil with

adequate drainage and aeration and reasonable fertility. Struc-

tural soil meets engineers’ load-bearing requirements for base

courses under pavement, and enables healthy root growth. It is a

mixture of load-bearing stone and soil. Uniformly graded 3/4”-1

1/2” angular crushed stone ensures the greatest porosity. Soil

with a minimum of 20% clay and 2-5% carbon content is recom-

mended. It should be used to a depth of 24-36”.

Graphic credit: Nina Bas-

suk, Urban

Horticulture Institute,

Cornell University.

Developer’s Guide to Low Impact Development, City of Greenfield, MA

Photocredit: Nina Bas-

suk, Urban

Horticulture Institute,

Cornell University.

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Resources

City of Greenfield Department of Planning and Development: http://greenfield-ma.gov/p/29/Department-of-Planning--Development Find

the most recent Zoning Ordinance, Subdivision Regulations, and City planning documents.

General Information:

Franklin Regional Council of Governments (FRCOG) Green Infrastructure webpage: http://frcog.org/program-services/natural-resources-

planning/green-infrastructure-and-low-impact-development/ Includes information on projects and initiatives in Franklin County.

United States Environmental Protection Agency (EPA) Green Infrastructure website: http://water.epa.gov/infrastructure/

greeninfrastructure/

Massachusetts Smart Growth / Smart Energy Toolkit: http://www.mass.gov/envir/smart_growth_toolkit/pages/mod-lid.html

Design Guides and Specifications:

Massachusetts Stormwater Handbook: http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-

handbook.html See Volume 2, Chapter 2: Stormwater Best Management Practices for design specifications.

Massachusetts Clean Water Toolkit: http://prj.geosyntec.com/npsmanual/default.aspx Also known as the Massachusetts Nonpoint Source

Pollution Management Manual, the Toolkit is an interactive tool that includes information about nonpoint source pollution, a selector tool

for choosing appropriate best management practices by criteria, and BMP factsheets.

Massachusetts Watershed Coalition, Community Guide to Growing Greener: http://commonwaters.org/resources/community-guide-to-

growing-greener Describes design and construction practices for stormwater management, erosion and sedimentation control, land-

scape design, and site planning.

University of New Hampshire (UNH) Stormwater Center: http://www.unh.edu/unhsc/. Includes information on research of stormwater

technologies, design, workshops, and economic benefits.

CU-Structural Soil®: A Comprehensive Guide: http://www.hort.cornell.edu/uhi/outreach/pdfs/CU-Structural%20Soil%20-%20A%

20Comprehensive%20Guide.pdf, Nina Bassuk, Urban Horticulture Institute, Cornell University. Provides guidance on the application and

design specifications of using structural soil.